Subansiri Upper Hydroelectric Project: Key Fact, Background, Environmental Significance, Subansiri River, Disaster Risk, Importance and Challenges

Why in news?

• The Subansiri Upper Hydroelectric Project (SUHEP) in Arunachal Pradesh has moved a step closer to environmental clearance after the Expert Appraisal Committee (EAC) of the Ministry of Environment, Forest and Climate Change recommended the project for environmental clearance.

Key Facts

Historical Background 

• Initially, projects in this stretch were conceived in the 1980s as a much larger integrated project, primarily aimed at flood moderation.
• The concept was subsequently divided into different projects, including Subansiri Upper, Middle Subansiri/Kamala and Subansiri Lower. 
• The Subansiri Upper project was initially allotted to NHPC in 2000. Its feasibility report was submitted in 2002 and approved by the Central Electricity Authority.
• The project later went through changes in its developer arrangements before being allotted again to NHPC by the Ministry of Power in 2021. 
• An agreement between the Arunachal Pradesh government and NHPC for development of the project was signed in August 2023.

What is the Subansiri Upper Hydroelectric Project?

• The project is planned near Menga, approximately 20 km from Daporijo, the headquarters of Upper Subansiri district.
• It is being developed by NHPC Limited and has two major objectives:
  • Hydroelectric power generation
  • Flood moderation
• The project will have an installed capacity of 1,605 MW and envisages construction of a massive storage dam on the Subansiri River.

Why is the Project environmentally significant?

• The biggest concern associated with the project is the scale of forest diversion required for its construction.
• According to the EAC proceedings, approximately 2,733 hectares of forest land would need to be diverted and around 1.35 lakh trees may have to be felled.
• The EAC observed that such extensive tree felling could have implications for forest structure, habitat continuity, biodiversity, movement of wildlife and ecosystem services. 
• The issue is particularly important because Arunachal Pradesh forms part of the ecologically sensitive Eastern Himalayan region, known for its rich biodiversity and forest ecosystems.

What has the EAC recommended?

• The plan is expected to include measures like: 
  • Avoidance and minimisation of tree felling wherever possible
  • Phased restoration of disturbed areas
  • Assisted Natural Regeneration
  • Plantation of suitable native species
  • Soil and moisture conservation
  • Control of invasive species
  • Appropriate compensatory measures

Subansiri River: Why is it important?

• The Subansiri River is one of the major tributaries of the Brahmaputra River. It originates in the Tibetan region and flows through Arunachal Pradesh before entering Assam and joining the Brahmaputra.
• The Subansiri basin has significant hydropower potential because of:
  • Steep Himalayan gradients
  • High river discharge
  • Large elevation differences
  • Significant rainfall and snow/glacial contribution

Cascade of Hydropower Projects

• Several hydroelectric projects have been proposed or developed in the wider Subansiri river system.
• Immediately upstream of Subansiri Upper is the proposed Dengser Hydroelectric Project. Further upstream, projects including Oju, Niare, Naba and Nalo have been proposed.
• Downstream lies the Subansiri Lower Hydroelectric Project, while the Kamala Hydroelectric Project, earlier known as the Middle Subansiri project, is being developed on the Kamala River, a tributary of the Subansiri.

Supreme Court and the Subansiri Projects

• While considering the Subansiri Lower project, the Standing Committee of the National Board for Wildlife (NBWL) had earlier imposed a condition concerning the construction of projects upstream.
• The Arunachal Pradesh government subsequently approached the Supreme Court regarding this condition. 
• In August 2009, the Supreme Court directed that proposals for projects upstream of the Subansiri River should be considered independently on their own merits by the relevant wildlife appraisal mechanism when submitted by project proponents.
• The EAC referred to this legal background while considering the Subansiri Upper project.

Disaster Risk and GLOF Assessment

• During the appraisal of the Subansiri Upper project, the EAC noted assessments relating to Glacial Lake Outburst Floods (GLOFs), Peak flood discharge, Possible dam-break scenarios and Potential downstream impacts, including implications for the Subansiri Lower project. 

Importance for India

• Renewable Energy Generation: With a capacity of 1605 MW, the project could add a substantial amount of hydropower capacity to India's electricity system. Hydropower can complement variable renewable sources such as solar and wind because reservoir-based projects can provide relatively flexible electricity generation.
• Flood Moderation: This is significant because the Brahmaputra basin, particularly parts of Assam, experiences recurrent flooding.
• Energy Transition: Large hydropower projects form part of India's broader efforts to expand non-fossil electricity capacity and reduce dependence on fossil fuels.
• Development of the Northeast: Large infrastructure projects can potentially improve connectivity, investment, employment and supporting infrastructure in remote Himalayan regions, although their social and environmental impacts require careful management.

Major Concerns

• Forest and Biodiversity Loss: Felling more than 1.35 lakh trees could affect habitat continuity, wildlife movement and ecosystem services.
• Cumulative Impact: A cascade of several dams within the same river basin raises the question of cumulative ecological impacts, rather than impacts of individual projects alone.
• Geological Vulnerability: The Himalayas are geologically young and tectonically active. Therefore, large infrastructure projects require rigorous seismic and geological assessments.
• Downstream Impact: Changes in natural river flow and sediment transport may influence downstream river ecology and communities.

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